B1-7 Personal pronouns (stressed and unstressed)

The difference between stressed and unstressed pronouns is that stressed pronouns can act as the subject of a sentence and as its object. On the other hand, unstressed pronouns can never act as the subject.

When pronouns come with a preposition, we use subject pronouns (except for the first and second person singular, ‘yo’ and ‘tú’). These become ‘mí’ and ‘ti’ (stressed pronouns).
ex. Me han hablado muy mal de ti.
Me han hablado muy mal de ellas.
Me han hablado muy mal de vosotros.